- Add Add and Del methods to Client for dynamic host management.
- Add RWMutex to Client to protect the devices map.
- Add Transport to Config to allow mocking HTTP transport in tests.
- Add getDeviceByHost helper to centralize device lookup locking.
- Refactor GetAll* methods to snapshot host keys before iteration to avoid concurrent map read/write panic.
- Add tests for thread safety and Add/Del functionality.
